Method of generating code sequence and method of transmitting signal using the same

ABSTRACT

A method of generating a code sequence and method of adding additional information using the same are disclosed, by which a code sequence usable for a channel for synchronization is generated and by which a synchronization channel is established using the generated sequence. The present invention, in which the additional information is added to a cell common sequence for time synchronization and frequency synchronization, includes the steps of generating the sequence repeated in time domain as many as a specific count, masking the sequence using a code corresponding to the additional information to be added, and transmitting a signal including the masked sequence to a receiving end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/033,498, filed on Feb. 23, 2011, now U.S. Pat. No. 8,830,983, whichis a continuation of U.S. patent application Ser. No. 12/158,657, filedon Oct. 28, 2008, now U.S. Pat. No. 7,916,759, which is the NationalStage filing under 35 U.S.C. §371 of International Application No.PCT/KR2006/005598, filed on Dec. 20, 2006, which claims the benefit ofearlier filing date and right of priority to Korean Application Nos.10-2006-0130507, filed on Dec. 20, 2006, 10-2006-0081035, filed on Aug.25, 2006, and 10-2005-0126307, filed on, Dec. 20, 2005, and also claimsthe benefit of U.S. Provisional Application Serial Nos. 60/828,759,filed on Oct. 9, 2006, 60/847,780, filed on Sep. 27, 2006, and60/827,022, filed on Sep. 26, 2006, the contents of which are all herebyincorporated by reference herein in entirety.

TECHNICAL FIELD

The present invention relates to a synchronization associated channel,and more particularly, to a method of generating a code sequence andmethod of adding additional information using the same. Although thepresent invention is suitable for a wide scope of applications, it isparticularly suitable for generating a code sequence usable for achannel for synchronization and configuring a synchronization channelusing the generated sequence.

BACKGROUND ART

First of all, a synchronization channel (hereinafter abbreviated SCH) asan example of a specific channel is explained as follows.

In order for a user equipment to communicate with a base station in amobile communication system, the user equipment primarily performssynchronization with the base station on SCH and then secondarilyperforms a cell search. A series of process for performingsynchronization with a base station and obtaining an ID of a cell towhich a user equipment belongs is called a cell search.

Generally, a cell search is classified into an initial cell searchexecuted in case of a user equipment's ‘power on’ in an initial mode anda neighbor cell search performed by a user equipment in a connectionmode (i.e., normal mode) or idle mode to search a neighbor base station.

FIG. 1 is a flowchart of a cell search procedure.

If the 3GPP LTE system is taken as an example among variouscommunication systems, the SCH structure for the cell search isclassified into a hierarchical structure and a non-hierarchicalstructure according to a time symbol synchronization and cell searchmethod.

And, a cell ID obtaining method is classified into a first method ofsearching cell groups and searching reference signals for a final cellID and a second method of obtaining a cell ID from SCH only.

In case of the first method, a cell group ID is obtained from SCH. Incase of the second method, a final cell ID (i.e., cell ID) is obtainedfrom SCH.

SCH following the hierarchical structure is explained as follows.

First of all, the SCH following the hierarchical structure is classifiedinto a primary SCH (hereinafter abbreviated P-SCH) and a secondary SCH(S-SCH) like SCH of WCDMA.

The P-SCH is a channel on which all cells or sectors use the same signaland performs initial symbol synchronization and frequencysynchronization. A signal value of P-SCH is already known by all userequipments. So, initial time symbol synchronization can be executed byperforming cross-correlation between a received signal and apredetermined signal. Such a series of procedures are calledcross-correlation based detection.

After time, symbol and frequency synchronizations have been obtained,cell ID or cell group ID detection is performed at a position of S-SCHpreviously indicated by timing synchronization information obtained fromP-SCH.

Meanwhile, a method of multiplexing P-SCH and S-SCH can be classifiedinto TDM, FDM and CDM.

FIG. 2 is a structural block diagram of SCH following a hierarchicalstructure.

An example shown in FIG. 2 corresponds to an example of multiplexing byTDM. Positions of P-SCH and S-SCH and a count of OFDM symbols includingP-SCH and S-SCH may differ from the case shown in FIG. 2.

Referring to FIG. 2, SCH is generated via two OFDM symbols. A radioframe includes 20 sub frames, and a specific radio frame is selected totransmit SCH only.

In the example shown in FIG. 2, first and second OFDM symbol provideSCH. Yet, an OFDM symbol which provides SCH can be another OFDM symbol,e.g., a last OFDM symbol.

SCH following the non-hierarchical structure is explained as follows.

First of all, a non-hierarchical SCH is characterized in having arepetitive waveform within an OFDM symbol in time domain. This enables auser equipment to perform a blind detection of initial time symbolsynchronization through auto-correlation of a received signal using therepetitive characteristic of signal. And, this detection is calledauto-correlation based detection.

After completion of the time and frequency synchronizations, cell IDdetection or cell group ID detection are carried out at a position ofthe detected SCH.

FIG. 3 is a structural block diagram of SCH following a non-hierarchicalstructure. An OFDM symbol or subframe to form SCH can be freely changed.

In the above-explained hierarchical structure, cross-correlation baseddetection can be carried out based on Formula 1.

$\begin{matrix}{\mspace{79mu}{{{\hat{d} = {\underset{d}{\arg\;\max}\left\{ {R(d)} \middle| {0 \leq d \leq {N_{f} - 1}} \right\}}}{{R(d)} = {\sum\limits_{p = 1}^{P}{\sum\limits_{q = 1}^{Q}\left( {\left( {\sum\limits_{m = 1}^{M}{{\sum\limits_{n = {{({m - 1})}L}}^{{mL} - 1}{{S^{*}(n)}{r_{p,q}\left( {n + d} \right)}}}}^{2}} \right)/\left( {\sum\limits_{n = 0}^{N - 1}{{r_{p,q}\left( {n + d} \right)}}^{2}} \right)} \right)}}}}\mspace{79mu}\left( {N = {ML}} \right)}\;} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Formula 1, ‘R(d)’ is a cost function to find a start point forsynchronization acquisition, ‘{circumflex over (d)}’ is a value tomaximize the R(d), and ‘N_(f)’ is a length of a radio frame. ‘P’indicates a count of symbols used for averaging. ‘Q’ indicates a countof receiving antennas of a user equipment. ‘L’ indicates a count ofParts for M-partial correlation. ‘N’ indicates a point of FFT/DFToperation. ‘r_(p,q)(n)’ indicates a signal received by a q^(th)receiving antenna in a p^(th) P-SCH symbol. And, ‘S(n)’ indicates aknown sequence inserted in P-SCH. In this case, in the environment wherefrequency offset exists, if symbol synchronization via cross-correlationbased detection is simply carried out, performance is degraded. So,M-partial correlation can be applied. [Y.-P. E. Wang and T. Ottosson,“Cell search in W-CDMA”, Selected Areas in Communications, IEEE Journalon, vol. 18, pp. 1470-1482, August 2000.]

In the hierarchical structure shown in FIG. 2, a method of estimatingfrequency offset can be represented as Formula 2.

$\begin{matrix}{{\Delta\; f} = {\frac{f_{s}}{\pi\; N}\arg\left\{ {- {\sum\limits_{p = 1}^{P}{\sum\limits_{q = 1}^{Q}{\left\lbrack {\sum\limits_{n = 0}^{{N/2} - 1}\left( {{S^{*}(n)}{r_{p,q}\left( {n + \hat{d}} \right)}} \right)} \right\rbrack^{*}\left. \quad\left\lbrack {\sum\limits_{n = {N/2}}^{N - 1}\left( {{S^{*}(n)}{r_{p,q}\left( {n + \hat{d}} \right)}} \right)} \right\rbrack \right\}}}}} \right.}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Formula 2, ‘f_(s)’ means a sampling frequency and ‘arg{ }’ means aphase component for a complex number. And, the frequency offset isgenerated from the difference between frequencies generated byoscillators provided to a base station and a user equipment,respectively.

And, the auto-correlation based detection used for the non-hierarchicalstructure shown in FIG. 3 is represented as Formula 3.

$\begin{matrix}{{R(d)} = {\sum\limits_{p = 1}^{P}{\sum\limits_{q = 1}^{Q}\left( {{{\sum\limits_{n = 0}^{{N/2} - 1}{{r_{p,q}^{*}\left( {n + d} \right)}{r_{p,q}\left( {n + d + {N/2}} \right)}}}}^{2}/{\sum\limits_{n = 0}^{{N/2} - 1}\left( {{{r_{p,q}\left( {n + d} \right)}}^{2} + {{r_{p,q}\left( {n + d + {N/2}} \right)}}^{2}} \right)}} \right)}}} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack\end{matrix}$

And, the frequency offset can be estimated in the non-hierarchicalstructure in a following meaner of Formula 4.

$\begin{matrix}{{\Delta\; f} = {\frac{f_{s}}{\pi\; N}\arg\left\{ {- {\sum\limits_{p = 1}^{P}{\sum\limits_{q = 1}^{Q}{\sum\limits_{n = 0}^{\frac{N}{2 - 1}}{\left\lbrack {r_{p,q}\left( {n + \hat{d}} \right)} \right\rbrack^{*}\left\lbrack {r_{p,q}\left( {n + \hat{d} + \frac{N}{2}} \right)} \right\rbrack}}}}} \right\}}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The cell search method uses the same method for both of the hierarchicalstructure and the non-hierarchical structure.

Comparison between the hierarchical SCH and the non-hierarchical SCH isexplained as follows.

First of all, communication systems are classified into a synchronousnetwork and an asynchronous network. In particular, the synchronousnetwork is a network having the same transmission start time for allsectors. Yet, in the asynchronous network, although sectors within oneNode-B have the same transmission start time, a transmission start timeis random between Node-Bs.

In case that both of the synchronous network and the asynchronousnetwork need to be supported, the hierarchical SCH is preferably used.

FIG. 4 is a diagram of performance comparison between hierarchical SCHand non-hierarchical SCH in a synchronous system. And, FIG. 5 is adiagram of performance comparison between hierarchical SCH andnon-hierarchical SCH in an asynchronous system.

Referring to FIG. 4 and FIG. 5, a case of using a hierarchical structureimproves performance of cell search. Yet, in the hierarchical structure,cross-correlation detection should be used for timing synchronizationacquisition and frequency offset estimation performance of thehierarchical structure is inferior to that of a non-hierarchicalstructure. FIG. 6 is a diagram of residual frequency offset error in asynchronous system, and FIG. 7 is a diagram of residual frequency offseterror in an asynchronous system.

In brief, each of the hierarchical SCH and the non-hierarchical SCH hasits own problems.

To solve these problems, the hybrid SCH scheme has been proposed. In thehybrid SCH scheme the hierarchical SCH and the non-hierarchical SCH arecombined together.

FIG. 8 is a diagram to explain a hybrid SCH scheme.

Referring to FIG. 8, a hybrid SCH includes P-SCH and S-SCH like thehierarchical SCH. Yet, P-SCH is assigned to a frequency index with aspecific interval in a specific OFDM symbol. In other words, a sequenceincluded in P-SCH is configured in a manner that a specific waveform isrepeated in time domain by a prescribed count.

Meanwhile, S-SCH is configured in a same manner of the hierarchical SCH.

In case of the hybrid SCH, P-SCH is configured by a cell commonsequence. Yet, by allocating the respective sequences (P₀, P₁, P₂, . . ., P_(N-2), P_(N-1)) corresponding to P-SCH to a frequency domain with aspecific interval, cell search and frequency offset characteristics areenhanced.

Formula 5A shows a method of estimating a synchronization in a hybridSCH and Formula 5B shows a method of estimating a frequency offset.

$\begin{matrix}{\mspace{79mu}{{{{\hat{d} = {\arg\limits_{d}\;\max\left\{ {R(d)} \middle| {0 \leq d \leq {N_{f} - 1}} \right\}}}{R(d)}} = {{\left( {\sum\limits_{m = 0}^{M - 1}{{\sum\limits_{m = {mL}}^{{{({m + 1})}L} - 1}{{p^{*}(n)}{r\left( {d + n} \right)}}}}^{2}} \right)/\left( {\sum\limits_{n = 0}^{{N_{fft}/2} - 1}{{r\left( {d + n} \right)}}^{2}} \right)} + {\left( {\sum\limits_{m = 0}^{M - 1}{{\sum\limits_{n = {mL}}^{{{({m + 1})}L} - 1}{{p^{*}\left( {\frac{N_{fft}}{2} + n} \right)}{r\left( {\frac{N_{fft}}{2} + d + n} \right)}}}}^{2}} \right)/\left( {\sum\limits_{n = 0}^{{N_{fft}/2} - 1}{{r\left( {\frac{N_{fft}}{2} + d + n} \right)}}^{2}} \right)}}}\mspace{79mu}\left( {{N_{fft}/2} = {ML}} \right)}} & \left\lbrack {{Formula}\mspace{14mu} 5A} \right\rbrack \\{\hat{f} = {\frac{N_{fft}}{2\pi\;{N_{fft}/N_{rep}}}\arg\left\{ {\sum\limits_{n = 0}^{{N_{fft}/2} - 1}{\left\lbrack {r\left( {\hat{d} + n} \right)} \right\rbrack^{*}\left\lbrack {r\left( {\hat{d} + n + {N_{fft}/2}} \right)} \right\rbrack}} \right\}}} & \left\lbrack {{Formula}\mspace{14mu} 5B} \right\rbrack\end{matrix}$

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to a method of generatinga code sequence and method of adding additional information using thesame that substantially obviate one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a method of generatinga synchronization channel carrying additional information.

Another object of the present invention is to provide a method ofgenerating a sequence for a synchronization channel.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofadding additional information to a sequence for synchronization, inwhich the additional information is added to a cell common sequence fortime synchronization and frequency synchronization, according to thepresent invention includes the steps of generating the sequence repeatedin time domain as many as a specific count, masking the sequence using acode corresponding to the additional information to be added, andtransmitting a signal including the masked sequence to a receiving end.

Preferably, the code includes either an orthogonal code or aquasi-orthogonal code.

Preferably, the code to be used in the masking step corresponds to theadditional information by one-to-one.

Preferably, the masking step includes the step of multiplying thesequence by the code in the time domain.

Preferably, the sequence generating step includes the steps ofallocating a sample included in the sequence to a frequency index with aconstant interval in frequency domain, respectively and transforming aresult of the allocating step into a time domain signal.

More preferably, the interval depends on the specific count.

Preferably, the masked sequence is transmitted on P-SCH (primarysynchronization channel).

Preferably, the transmitting step includes the step of transmitting thesignal using a plurality of orthogonal subcarriers.

Preferably, the additional information includes various kinds ofinformation necessary for communications between nodes.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of adding additionalinformation to a sequence for synchronization, in which the additionalinformation is added to a cell common sequence for time synchronizationand frequency synchronization, includes the steps of allocating samplesincluded in the sequence to a specific frequency index according to theadditional information to be added and transmitting the sequence to areceiving end by transforming the sequence into a time domain signal.

Preferably, the allocating step includes the step of allocating thesamples to the frequency index with a constant interval.

More preferably, the constant interval depends on a size of theadditional information.

Preferably, the additional information includes various kinds ofinformation necessary for communications between nodes.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of adding additionalinformation to a sequence for a synchronization channel includes thesteps of generating the sequence for the synchronization channel,performing micro constellation modulation to rotate a phase of thesequence according to a phase value corresponding to the additionalinformation to be added, and transmitting a signal including themicro-constellation-modulated sequence to a receiving end.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of transmitting a signal, inwhich a transmitting side of a communication system performs dataprocessing on a code sequence into a form requested by the communicationsystem for at least one of initial synchronization acquisition, cellsearch and channel estimation and then transmits the data-processedsignal to a receiving side of the communication system, includes thestep of generating the code sequence by masking a repetitive codesequence with a specific orthogonal code, wherein the repetitive codesequence comprises at least twice repeated unit code sequences, eachhaving a length L.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of generating a codesequence, which is used for at least one use of initial synchronizationacquisition, cell search and channel estimation, includes the steps ofgenerating a unit code sequence set including unit code sequences, eachhaving a length of L, by code generating algorithm according to a codetype, generating a repetitive code sequence set including repetitivecode sequences generated from repeating each of the unit code sequencesbelonging to the unit code sequence set twice at least, and masking eachof the repetitive code sequences belonging to the repetitive codesequence set with a specific orthogonal code.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a flowchart of a cell search procedure;

FIG. 2 is a structural block diagram of SCH following a hierarchicalstructure;

FIG. 3 is a structural block diagram of SCH following a non-hierarchicalstructure;

FIG. 4 is a diagram of performance comparison between hierarchical SCHand non-hierarchical SCH in a synchronous system;

FIG. 5 is a diagram of performance comparison between hierarchical SCHand non-hierarchical SCH in an asynchronous system;

FIG. 6 is a diagram of residual frequency offset error in a synchronoussystem;

FIG. 7 is a diagram of residual frequency offset error in anasynchronous system;

FIG. 8 is a diagram to explain a hybrid SCH scheme;

FIG. 9 is an exemplary block diagram of P-SCH inserted by the firstmethod of the present embodiment;

FIG. 10 shows a flow chart for generating P-SCH in time domain andinserting additional information;

FIGS. 11A to 11C are block diagrams of examples of a sequence on whichthe masking is performed by the first method of the present embodiment;

FIG. 12 is a flow chart explaining steps of the second method;

FIG. 13 is a diagram to explain a method of allocating a specificsequence in frequency domain;

FIG. 14 is a flow chart explaining third method;

FIG. 15 is a block diagram of P-SCH and S-SCH in which additionalinformation will be included;

FIG. 16A and FIG. 16B are block diagrams to explain examples of adding1-bit additional information;

FIGS. 17A to 17D are block diagrams to explain examples of adding 2-bitadditional information, in which additional information is added toS-SCH;

FIG. 18 is a diagram of examples by both a third method of the presentembodiment and micro-constellation modulation;

FIG. 19 is a flowchart of a method of generating a sequence for asynchronization channel according to an embodiment of the presentinvention;

FIG. 20 is a block diagram of a transmitting apparatus according to anembodiment of the present invention;

FIG. 21 is a block diagram of a communication apparatus for transmittingP-SCH according to the present invention;

FIG. 22A and FIG. 22B are diagrams of frequency and time domain signalsof a short preamble used by IEEE 802.11a, respectively;

FIG. 23A and FIG. 23B are diagrams of auto-correlation characteristicsof a short preamble used by IEEE 802.11a in frequency and time domains,respectively;

FIG. 24 is a flowchart of a code sequence generating method according toone preferred embodiment of the present invention;

FIG. 25 is a diagram to explain a masking method by Hardamard codesaccording to one preferred embodiment of the present invention;

FIGS. 26 to 31 are graphs of performance curves to estimate performanceof preferred embodiments of the present invention, respectively; and

FIG. 32 and FIG. 33 are block diagrams to explain a signal transmittingmethod and a transmitting apparatus according to one preferredembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

The present embodiment relates to synchronization channels. And, thesynchronization channels can be classified into P-SCH and S-SCH. Thepresent embodiment proposes a method of having additional informationincluded in the synchronization channel. And, the present embodimentproposes a method of generating a sequence usable for thesynchronization channel.

First of all, a method of having additional information included in asynchronization channel according to a first embodiment of the presentinvention is explained.

Secondly, a method of generating a sequence usable for a synchronizationchannel according to a first embodiment of the present invention isexplained.

First Embodiment

In case of the aforesaid hierarchical SCH or hybrid SCH, P-SCH and S-SCHare used. And, the P-SCH is a cell common sequence. In particular, theP-SCH is provided by all base stations or sectors through a samesequence. In other words, the P-SCH is corresponding to the sequencealready known to a user equipment and is used to acquire timingsynchronization and frequency synchronization.

In case of the hierarchical or hybrid SCH, cell ID and other specificcell information can be obtained through S-SCH or various kinds ofcontrol channels, e.g., BCH, etc.

In the present embodiment, a method of adding additional information toa channel for synchronization such as P-SCH, S-SCH, hybrid SCH and thelike.

The following method can be mainly divided into a method of addingadditional information using masking by codes, a method of addingadditional information using micro constellation modulation, and amethod using both masking and micro constellation modulation.

First to third methods explained in the following description areexamples of the method using masking by codes, which describes examplesof adding additional information to P-SCH among synchronizationchannels. Since the method using masking by codes is applicable varioussynchronization channels, the following examples of P-SCH applicationare just exemplary. So, the present invention is not limited to theexamples of the P-SCH application.

Despite the insertion of additional information into P-SCH according tothe embodiment of the present invention, complexity according tosynchronization estimation does not increase. And, the related artsynchronization estimating method can be used as it is. Moreover, theinserted additional information of the present embodiment can be easilydetected in various ways.

1. First Method

A first method according to the present embodiment includes the steps ofgenerating P-SCH in time domain and inserting additional information.

In the first method, the P-SCH generating step and the additionalinformation inserting step are preferably performed in the time domain.

FIG. 9 is an exemplary block diagram of P-SCH inserted by the firstmethod of the present embodiment.

Referring to FIG. 9, it is able to assign P-SCH to 128 (=N) subcarriers.Preferably, P-SCH according to the present embodiment is generated in amanner that specific sequences (A) are repeated in time domain. Thesequence (A) includes 64 samples A₀ to A₆₃. And, the 64 samples A₀ toA₆₃ are allocated to the subcarriers in frequency domain, respectively.FIG. 9 shows that two sequences (A) are repeated in the time domain.

FIG. 10 shows a flow chart for generating P-SCH in time domain andinserting additional information.

The steps of generating P-SCH in time domain and inserting additionalinformation can be divided into the following steps.

In a first step S101, a P-SCH sequence is inserted in time domain. InFIG. 9, the P-SCH is generated by repeating a specific sequence (A)twice in time domain.

Preferably, the specific sequence (A) is P-SCH according to theaforesaid hybrid SCH. Yet, the specific sequence (A) can be a randomsequence. In particular, the specific sequence (A) can be the P-SCHaccording to the hierarchical SCH.

In a second step S102, masking is carried out on a specific code. Inparticular, masking is carried out on the sequence generated in the stepS101. There are various results from performing masking on the specificsequence. And, the result of masking represents specific additionalinformation.

The masking means a work for performing data processing according to thespecific code. No limitation is put on a type of the specific code and atype of the data processing. Preferably, the code used for the maskingis an orthogonal code or a pseudo-orthogonal code. Preferably, themasking operation means a work of multiplying each of the samples of thesequence generated in the step S101 by the code.

FIGS. 11A to 11C are block diagrams of examples of a sequence on whichthe masking is performed by the first method of the present embodiment.

FIG. 11A shows a result of performing masking on the sequence shown inFIG. 9 using Walsh codes.

Referring to FIG. 11A, in a case of masking the sequence shown in FIG. 9using code [1,1], it can be decided that additional information is setto ‘0’. In a case of masking the sequence shown in FIG. 9 using code[1,−1], it can be decided that additional information is set to ‘1’.

FIG. 11B shows a result of performing masking on the sequence shown inFIG. 9 using random codes.

Referring to FIG. 11B, the random code includes a sample having a sizeof ‘1’ and a phase value of ‘0° ’ or ‘180° ’. In a case of masking thesequence shown in FIG. 9 using code [1,1], it can be decided thatadditional information is set to ‘0’. In a case of masking the sequenceshown in FIG. 9 using code [1,−1], it can be decided that additionalinformation is set to ‘1’.

FIG. 11C shows a result of performing masking on the sequence shown inFIG. 9 using DFT sequence.

Referring to FIG. 11C, in case of performing masking using DFT sequence

${{c(n)} = {\mathbb{e}}^{{- {j2\pi}}\frac{r}{N}}},\left( {{r = 0},1,\ldots\mspace{14mu},{N - 1}} \right),$like the contents of FIG. 11C, it can be decided that additionalinformation is set to ‘0’ if r=0. And, it can be decided that additionalinformation is set to ‘1’.

The cases of FIGS. 11A to 11C are the examples of performing maskingusing two kinds of codes. Since the examples shown in FIGS. 11A to 11Care just provided for convenience of explanation, it is able to performthe masking using an arbitrary count of codes. Namely, it is able to addadditional information constructed with arbitrary bits. For instance,2-bit additional information can be added by incrementing a count ofWalsh codes into 4. And, 3-bit additional information can be added byincrementing a count of Walsh codes into 8. In case of DFT sequence, itis able to generate additional information having a random size byfreely adjusting sizes of ‘r’ and ‘N’. In case of arbitrary codes, it isable to adjust a size of additional information by adjusting a type ofeach code.

The sequence generated in the second step S102 of FIG. 10 is provided toa user equipment for synchronization estimation. The sequence accordingto the present embodiment is usable for various communication systems.Preferably, the sequence according to the present embodiment is used fora system that transmits a signal via a plurality of orthogonalsubcarriers.

If a system, to which the present embodiment is applied, is not theOFDM/OFDMA system, a corresponding sequence is transmitted by passingthrough a low pass filter (LPF) corresponding to a transmissionbandwidth. If DC subcarrier is not taken into consideration by theOFDM/OFDMA specifications, it is able to have the corresponding sequencepass through the LPF without the subcarrier insertion.

Meanwhile, in case that a system, to which the present embodiment isapplied, is used for a system (e.g., OFDM, OFDMA, SC-FDMA) that uses aplurality of orthogonal subcarriers, the following steps S103 to S106are preferably executed in addition. In particular, since the systemusing a plurality of orthogonal subcarriers needs a DC subcarrier toeliminate a DC component and a guard band subcarrier to eliminate acomponent of a specific bandwidth, the following steps are preferablyexecuted in addition.

According to one embodiment of the present invention, a step S103 oftransforming a time domain sequence into a frequency domain sequence byFFT operation is explained as follows.

First of all, a method of transforming a time domain sequence into afrequency domain sequence in a multi-subcarrier system is represented asFormula 6, in which a length-N sequence generated in time domain istransformed into a frequency domain sequence by N-point FFT.

$\begin{matrix}{A_{k} = {\sum\limits_{n = 0}^{N - 1}{a_{n}{\mathbb{e}}^{{- {j2\pi}}\;{{kn}/N}}}}} & \left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

If each sample of the sequence generated by the steps S101 and S102 ofFIG. 10 is set to a_(n), a frequency domain sequence A_(k) is generatedby Formula 6.

A step S104 of inserting DC subcarrier and guard subcarrier according toone embodiment of the present invention is explained as follows.

First of all, in a specific OFDM communication method, insertion of DCsubcarrier and insertion of constant guard subcarrier can be required.In case that DC subcarrier and guard subcarrier have to be inserted tomeet the specifications defined in the specific OFDM communicationmethod, the step S104 is executed. The insertion of the DC subcarriermeans that data 0 is inserted in a subcarrier having a frequency of ‘0’in frequency domain to solve the problem caused by DC offset in an RFend of transmission/reception.

A step S105 of applying PAPR attenuation to the sequence havingundergone the above steps is explained as follows.

First of all, as the DC and guard subcarrier insertions or other dataprocessing are performed, PAPR of signals may increase. In the presentembodiment, PAPR attenuation can be re-executed to decrease theincreasing PAPR.

A step S106 of transforming the sequence into a time domain sequence byIFFT operation according to one embodiment of the present invention isexplained as follows.

First of all, the step S106 is to generate a final signal and isexecuted according to Formula 7. In this case, a generated sequence canbe utilized for execution of synchronization and detection anddiscrimination of signals.

$\begin{matrix}{a_{n} = {\frac{1}{N}{\sum\limits_{n = 0}^{N - 1}{A_{k}{\mathbb{e}}^{{j2\pi}\;{{kn}/N}}}}}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

2. Second Method

A second method in the following description is characterized inallocating and generating a sequence having specific-sized samples infrequency domain. For instance, in case of generating P-SCH using asequence A (A₀, A₁, A₂, . . . , A_(N-1)) including N samples, thesequence is generated in a following manner.

First of all, each sample included in a sequence is allocated to aspecific frequency index. In this case, the frequency index is toidentify a specific subcarrier. If samples are allocated to consecutivefrequency indexes, respectively, the samples are allocated toconsecutive frequency domains. If samples are allocated to frequencyindexes with specific interval, respectively, the samples are allocatedwith a frequency interval corresponding to the specific interval.

FIG. 12 is a flow chart explaining steps of the second method.

The second method includes the following steps.

First of all, DC subcarrier and guard subcarrier are inserted (S201). Inparticular, a component of a specific region in frequency domain ischanged into ‘0’.

Subsequently, a specific sequence A is allocated to the frequency domainwith a specific interval using the frequency indexes (S202).

A size of the specific interval can be freely set. For instance, it isable to allocate the sequence A with two frequency index intervals. Inthis case, it is able to allocate each sample of the sequence A toeither an even-order frequency index or an odd-order frequency index.

FIG. 13 is a diagram to explain a method of allocating a specificsequence in frequency domain.

In (a) of FIG. 13, if a specific sequence is allocated to consecutivefrequency indexes, a sequence (e.g., sequence including P₀ to P₁₂₇) intime domain is shown. In particular, a signal shown in (a) of FIG. 13corresponds to a result from allocating specific samples P₀ to P₁₂₇ to128 consecutive frequency indexes in frequency domain, respectively.

In case of allocating samples P₀ to P₁₂₇ to even-order frequencyindexes, it is able to configure a signal shown in (b) of FIG. 13 due tothe characteristics of over-sampling. In (b) of FIG. 13, a waveform B isrepeated. The repetitive waveform shown in (b) of FIG. 13 has a shapeobtained from compressing a waveform shown in (a) of FIG. 13. Since thesignal shown in (b) of FIG. 13 includes identical waveforms repeated intime domain, it can be represented as a [B|B] type signal.

Meanwhile, in case of allocating samples P₀ to P₁₂₇ to odd-orderfrequency indexes, it is able to configure a signal shown in (c) of FIG.13 due to the characteristics of DFT operation. The signal shown in (c)of FIG. 13 has a form different from that shown in (b) of FIG. 13. Inparticular, the signal shown in (c) of FIG. 13 has a different form in atime domain due to shift of frequency indexes. Because of thecharacteristics of DFT operation, the signal allocated to the odd-orderfrequency indexes has a [C|−C] shape in time domain.

In brief, it is able to allocate the sequence A to frequency indexeswith a specific interval. And, a count of waveform repetitions in timedomain and a waveform in time domain depend on a size of the intervaland the frequency indexes to which the sequence A is allocated.

In case that a base station generates P-SCH according to the secondmethod, the base station pre-decides a size of the interval and thefrequency indexes for the allocation. As mentioned in the foregoingdescription, since a waveform of signal transmitted by the base stationdepends on the size of the interval and the frequency indexes for theallocation, a method of generating a sequence in frequency domain needto be decided in advance. Besides, since the P-SCH need to be a cellcommon sequence, a predetermined sequence generating method ispreferably known to a user equipment in advance.

For instance, the base station decides to allocate the samples of thesequence A to the even-order frequency indexes. In this case, a signalhaving the [B|B] shape shown in (b) of FIG. 13 is generated. Since theuser equipment already knows that the [B|B] type signal will begenerated, it is able to perform cross-correlation based detection.Moreover, since the signal itself is repeated, auto-correlation baseddetection is possible as well.

The step S202 of FIG. 12 can be executed prior to the step S201 of FIG.12. So, there is no limitation put on an order between the step ofinserting the DC/guard subcarrier and the step of generating the P-SCHsequence in frequency domain. Yet, the step of generating the P-SCHsequence is preferably executed prior to a step S203 that is explainedin the following description.

In order to add additional information to the P-SCH, a transform into asignal in time domain needs to be performed. So, IFFT operation isperformed on the generated P-SCH (S203).

And, masking is carried out on a result of the step S203. In this case,the masking on the result of the step S203 is carried out by the stepS102.

After completion of the masking on the result of the step S203, thesteps S103 to S106 (shown in FIG. 10; not shown in FIG. 12) arepreferably carried out. In particular, the DC and guard subcarriers arepreferably inserted and the PAPR attenuation scheme is preferablyapplied. Although the DC and guard subcarriers have been alreadyinserted by the step S201, components except ‘0’ may be inserted in DCand guard subcarrier components. So, it is more preferable that ‘0’ isinserted or padded into the DC and guard subcarriers by executing thesteps S103 to S106.

In case of the guard subcarrier, it is able to obtain the same effect ofinserting a guard subcarrier using a specific filter (e.g., LPF).

If additional information is added by the first or second method, it isable to acquire synchronization using the conventional method in a samemanner. In particular, a receiving end (e.g., user equipment) acquirestiming synchronization via a conventional hierarchical or hybrid SCH.Moreover, since frequency synchronization corresponds to a functionhaving an arc tangent period of pi, it can be executed in the samemanner of the hybrid method according to the example of two repetitions.Namely, despite the addition of the additional information, the methodof acquiring the time and frequency synchronizations does not change.

The inserted additional information enables code information to bedetected by differential correlation represented as Formula 8 aftercompletion of the time and frequency synchronizations using the featureof the same absolute value.

$\begin{matrix}{\hat{b} = {{abs}\left\lbrack {{Re}\left\{ {\sum\limits_{n = 0}^{N_{fft}/2}{\left\lbrack {r\left( {\hat{d} + n} \right)} \right\rbrack^{*}\left\lbrack {r\left( {\hat{d} + n + {N_{fft}/2}} \right)} \right\rbrack}} \right\}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack\end{matrix}$

-   -   if {circumflex over (b)}≧0, decision to bit 0    -   else, decision to bit 1

According to Formula 8, it is able to reconstruct the additionalinformation using the features of a signal received by the receivingend.

The additional information can be reconstructed in various waysincluding the example shown in Formula 8.

For instance, it is able to reconstruct the additional information byhypothesis detection using cross-correlation. For example, atransmitting end (e.g., base station) inserts additional information bymaking using Walsh codes, [1,1] code corresponds to additionalinformation ‘0’, and [1,−1] code corresponds to additional information‘1’. In this case, a signal transmitted by the transmitting end has ashape of [A|A] or [A|−A] in time domain. And, since a waveform A isattributed to a cell common sequence, a user equipment has already knownthe waveform A. So, the user equipment is able to measure across-correlation value for the received signal via the [A|A] or [A|−A]signal. In particular, the user equipment is able to detect theadditional information by confirming a peak value though the hypothesisdetection using cross-correlation.

3. Third Method

The third method includes the step of generating P-SCH sequence infrequency domain and adding additional information in frequency domain.

FIG. 14 is a flow chart explaining third method.

In particular, DC and guard subcarriers are generated by the same stepof the step S201 (FIG. 12). And, a P-SCH sequence is generated with aspecific frequency index interval by considering the generated DC andguard subcarriers (S301). For instance, in case of generating P-SCHusing a sequence-A (A₀, A₁, A₂, . . . , A_(N-1)) including N samples, asequence is generated in a following manner.

First of all, if additional information is set to ‘0’, the N samples areallocated to even-order frequency indexes, respectively. In this case,as mentioned in the description of FIG. 13, the [B|B] waveform isgenerated in time domain. Meanwhile, if additional information is set to‘1’, the N samples are allocated to odd-order frequency indexes,respectively. In this case, as mentioned in the description of FIG. 13,the [C|−C] waveform is generated in time domain.

A size of the additional information is not limited. In case of adding2-bit additional information, four different waveforms are needed. So,it is able to allocate the N samples with an interval of four frequencyindexes. Through this, it is able to obtain four kinds of waveformsrepeated four times in time domain. Through this, it is able to addadditional information.

The P-SCH generated in frequency domain in the above manner is thentransformed into a time domain signal by IFFT operation according to thestep S106 as shown in FIG. 10.

In brief, the third method generates a plurality of cell commonsequences. And, each of a plurality of the cell common sequencesrepresents specific additional information. Unlike the first or secondmethod, the third method uses a plurality of the cell common sequences.In this case, synchronization acquisition in a user equipment can becarried out in a following manner.

First of all, the user equipment has already known a plurality of cellcommon sequences. N particular, the user equipment has already known the[B|B] signal for the case of allocating the N samples to the even-orderfrequency indexes and the [C|−C] signal for the case of allocating the Nsamples to the odd-order frequency indexes. And, the user equipment isable to acquire synchronization by finding cross-correlation between the[B|B] or [C|−C] signal and the received signal. Namely, even ifsynchronization is performed using cross-correlation, synchronization isacquired by performing hypothesis detection and additional informationis obtained.

Meanwhile, it is able to acquire synchronization using auto-correlationinstead of cross-correlation. Since a plurality of the cell commonsequences are allocated to the frequency indexes with a constantinterval, respectively, they have repetitive characteristics. So, theuser equipment is able to acquire synchronization using thecharacteristic of the signal that is repeated in time domain.

The first to third methods propose the scheme of performing the maskingon the sequence generated in frequency or time domain using specificcodes. And, a fourth method explained in the following descriptionproposes a method of adding additional information using fineconstellation modulation.

4. Fourth Method

A fourth method is characterized in performing micro-constellationmodulation in addition.

First of all, at least one information bit to be transmitted to areceiving end is constellation-mapped to one symbol. As constellationmapping according to the related art, there are QPSK, BPSK, 16QAM andthe like. At least one symbol (e.g., at least one QPSK symbol) isincluded in one OFDM symbol to be transmitted to the receiving end.

In this case, such a constellation mapping scheme as QPSK can be calledmacro-constellation modulation (i.e., conventional scheme). And, amodulation scheme applied for addition of additional information can becalled micro-constellation modulation or fine constellation modulation.

Symbols (e.g., QPSK symbols) having undergone macro-constellationmodulation are mapped to preset position on a constellation map. If atransmitting end transmits the symbols by rotating the symbols at apredetermined angle from the preset positions in addition, it can beseen that additional information is added through the additionallyrotated angle.

A basic concept of the fourth method of the present invention is to use2-step constellation mapping. In particular, macro-constellationmodulation is carried out on a sequence corresponding to a channel forsynchronization estimation. And, micro-constellation modulation isadditionally applied to the sequence having undergone themacro-constellation modulation. In this case, a method of themicro-constellation modulation is decided according to additionalinformation to be added.

The following method relates to a method adding normal M-bits.

The fourth method is applicable to a hierarchical SCH, anon-hierarchical SCH, or a hybrid SCH. For convenience of explanation, amethod of adding additional information to a hierarchical SCH isexplained in the following description. And, a case of multiplexingbetween P-SCH and S-SCH by TDM is explained. Yet, since the fourthmethod is applicable to various synchronization channel structures, itis not restricted by the following embodiment of the present invention.

FIG. 15 is a block diagram of P-SCH and S-SCH in which additionalinformation will be included.

Referring to FIG. 15, P-SCH and S-SCH can be generated according to theaforesaid method. In particular, the P-SCH and S-SCH can be generated infrequency or time domain. And, the P-SCH and S-SCH can be generated byrepetition in time domain or by allocating a sequence with a specificfrequency index interval in frequency domain.

According to the fourth method, an M-bit additional information addingmethod is carried out by multiplying a P-SCH part of the drawing by aphase function corresponding to the corresponding bits.

If a time domain sequence of P-SCH or S-SCH is p(n) (n=0, 1, 2, . . . ,N_(fft)−1), p_(bit(n)) after bit addition is represented as Formula 9A.

$\begin{matrix}{{P_{{bit}{(n)}} = {{\mathbb{e}}^{j\frac{2\pi\; m}{2^{M}}}{p(n)}}}{{n = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{2^{M} - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 9A} \right\rbrack\end{matrix}$

In Formula 9A, ‘m’ indicates an m^(th) additional information. Forinstance, in case of 1 bit of M=l, m=0 or 1 is possible. In case of 2bits of M=2, m=0, 1, 2, or 3 is possible.

In Formula 9A, ‘N’ indicates a length of sequence. ‘P_(bit(n))’indicates a time domain sequence to which additional information isadded. ‘P(n)’ indicates a time domain sequence before additionalinformation is added thereto. And, ‘n’ indicates a time domain sampleindex.

Formula 9A can be equivalently represented as Formula 9B. And, Formula9A is an example represented as a frequency domain sequence.

$\begin{matrix}{{P_{{bit}{(k)}} = {{\mathbb{e}}^{j\frac{2\pi\; m}{2^{M}}}{P(k)}}}{{k = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{2^{M} - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 9B} \right\rbrack\end{matrix}$

In Formula 9B, ‘P_(bit(k))’ indicates a frequency domain sequence towhich additional information is added in frequency domain. ‘P(k)’indicates a frequency domain sequence before additional information isadded thereto. And, ‘k’ indicates a frequency domain sample index.

FIG. 16A and FIG. 16B are block diagrams to explain examples of adding1-bit additional information.

Referring to FIG. 16A and FIG. 16B, it is able to add 1-bit additionalinformation by not varying phases of sequences included in P-SCH or byrotating the phases by 180° each.

The example shown in FIG. 16A indicates that additional informationcorresponding to ‘bit 0’ is included. And, the example shown in FIG. 16Bindicates that additional information corresponding to ‘bit 1’ isincluded.

Of course, it is able to add the additional information to each of P-SCHand S-SCH. It is able to add the additional to either P-SCH or S-SCH.And, it is also able to add the additional to both P-SCH and S-SCHsimultaneously. In case of M=1, the additional information to be addedincludes ‘+1’ and ‘−1’.

FIGS. 17A to 17D are block diagrams to explain examples of adding 2-bitadditional information, in which additional information is added toS-SCH for example.

Referring to FIGS. 17A to 17D, if M=2, additional informationcorresponds to ‘00’, ‘01’, ‘10’ or ‘11’. Of course, the additionalinformation can be applied to both P-SCH and S-SCH, either P-SCH orS-SCH, or P-SCH and S-SCH, respectively.

A method of searching additional information bits according to thepresent invention can be executed in various ways. For convenience ofexplanation, a method of detecting bits by inserting additionalinformation bit(s) into P-SCH and by performing channel estimation onS-SCH is explained.

If P-SCH and S-SCH, as shown in FIGS. 17A to 17D, are adjacent to eachother, it is able to assume that both of the SCHs undergo the samechannel. In this case, it is able to use a radio channel estimated asS-SCH in detecting additional information added to P-SCH.

For convenience, it is assumed that all subcarriers are used for afrequency part of P-SCH. And, it is also assumed that bit informationdetection is carried out after completion of time/frequencysynchronization with P-SCH and cell ID detection in S-SCH. In this case,a time domain signal received on P-SCH is represented as Formula 9C.r _(psch)(n)=p _(bit(n)) *h(n)+n(n)  [Formula 9C]

In Formula 9C, ‘h(n)’ indicates an impulse response of channel, ‘n(n)’indicates AWGN, and ‘*’ indicates a convolutional operation. A result ofFormula 9C can be represented as Formula 9D.r _(psch)(k)=P _(bit(k)) *H(k)+N(k)  [Formula 9D]

In Formula 9D, a signal indicates a frequency domain signal. In thiscase, ‘H(k)’ indicates a frequency response of channel and ‘N(k)’indicates AWGN. Time and frequency domain signals received on S-SCH arerepresented as Formula 9E and Formula 9F, respectively.r _(ssch)(n)=s(n)*h(n)+n(n)  [Formula 9E]R _(ssch)(k)=S(k)*H(k)+N(k)  [Formula 9F]

In Formula 9E and Formula 9F, ‘S(k)’ indicates an S-SCH signaltransmitted in frequency domain and ‘s(n)’ indicates an S-SCH signaltransmitted in time domain.

According to the above assumptions, channel estimation is executed inS-SCH. For instance, LS (least square) channel estimation can beexecuted according to Formula 9G.

$\begin{matrix}{\hat{H(k)} = \frac{R_{ssch}(k)}{S(k)}} & \left\lbrack {{Formula}\mspace{14mu} 9G} \right\rbrack\end{matrix}$

In Formula 9G, as mentioned in the foregoing description, since thedetection for cell ID has been completed, ‘S(k)’ is a value alreadyknown by the receiving end.

P-SCH is recovered as Formula 9H using the estimated radio channel.R _(eq)(k)=R _(psch)(k)/H({circumflex over (k)})=P _(bit(k))+N(k)/H({circumflex over (k)})  [Formula 9H]

It is able to detect added bit information by Formula 9I using‘R_(eq)(k)’ of which channel is compensated for.

$\begin{matrix}{\hat{m} = {\frac{M}{2\pi}\arg\left\{ {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{{R_{eq}(k)}{P(k)}}}} \right\}}} & \left\lbrack {{Formula}\mspace{14mu} 9I} \right\rbrack\end{matrix}$

In Formula 9I, ‘arg{ }’ indicates a phase component. And, ‘{ }’indicates a complex result value of correlation.

The aforesaid additional information adding method is applicable to thehybrid SCH or the non-hierarchical SCH. Namely, by an operation ofrotation by a phase corresponding to the additional information, it isable to add the additional information.

Hereinafter, a new method in which the first to third methods and thefourth method are combined together is proposed as follows.

A fifth method in the following description relates to a method ofadding additional information using both code masking andmicro-constellation modulation.

5. Fifth Method

First of all, it is preferable that a fifth method is applied to asequence having a repetitive structure in time domain. For instance, thefifth method is applied to hybrid SCH as follows.

Three methods of adding additional information by masking are proposed.The fifth method can use one of the three methods of adding additioninformation. Hereinafter, a method which uses the third method isexplained.

According to the aforesaid third method, in case of allocating asequence to an odd-order frequency index, additional information ‘1’ (or‘0’) is indicated. In case of allocating a sequence to an even-orderfrequency index, additional information ‘0’ (or ‘1’) is indicated.

According to the aforesaid explanation, if a sequence is allocated to anodd-order frequency index, a [C|−C] type waveform, as mentioned in (c)of FIG. 11, is formed in time domain. If a sequence is allocated to aneven-order frequency index, a [B|B] type waveform, as mentioned in (b)of FIG. 11, is formed in time domain.

In addition, micro-constellation modulation can be performed on thecorresponding result. In particular, by rotating a phase by 0° or 180°,it is able to add additional information.

FIG. 18 is a diagram of examples by both a third method of the presentembodiment and micro-constellation modulation.

Referring to FIG. 18, in case that added additional information is ‘00’,a sequence type is [B|B]. So, MSB of additional information is decidedas ‘0’. Meanwhile, since a phase is changed by 0° according tomicro-constellation modulation, LSB of additional information is decidedas ‘0’.

In case that added additional information is ‘01’, a sequence type is[B|B]. So, MSB of additional information is decided as ‘0’. Meanwhile,since a phase is changed by 180° according to micro-constellationmodulation, LSB of additional information is decided as ‘1’.

In case that added additional information is ‘10’, a sequence type is[C|−C]. So, MSB of additional information is decided as ‘1’. Meanwhile,since a phase is changed by 0° according to micro-constellationmodulation, LSB of additional information is decided as ‘0’.

In case that added additional information is ‘11’, a sequence type is[C|−C]. So, MSB of additional information is decided as ‘1’. Meanwhile,since a phase is changed by 180° according to micro-constellationmodulation, LSB of additional information is decided as ‘1’.

In order to detect additional information by the fifth method, it isdecided whether a sequence has a [B|B] type or a [C|−C] type and a phasevalue rotated by micro-constellation modulation is then calculated.

The fourth and fifth methods of the present embodiment are characterizedin using micro-constellation modulation.

In the above examples, a case that a count of added additionalinformations corresponds to a power of 2, which does not put limitationon the present embodiment.

Namely, it is able to convert Formula 9A to Formula 10A.

$\begin{matrix}{{P_{{bit}{(n)}} = {{\mathbb{e}}^{j\frac{2\pi\; m}{X}}{p(n)}}}{{n = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{X - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 10A} \right\rbrack\end{matrix}$

And, it is able to convert Formula 9B to Formula 10B.

$\begin{matrix}{{P_{{bit}{(k)}} = {{\mathbb{e}}^{j\frac{2\pi\; m}{X}}{P(k)}}}{{k = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{X - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 10B} \right\rbrack\end{matrix}$

In this case, Formulas 9C to 9H are applied as they are. And, Formula 9Iis converted to Formula 10C to be applied.

$\begin{matrix}{\hat{m} = {\frac{X}{2\pi}\arg\left\{ {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{{R_{eq}(k)}{P(k)}}}} \right\}}} & \left\lbrack {{Formula}\mspace{14mu} 10C} \right\rbrack\end{matrix}$

The above-explained example shown in FIG. 18 is applicable tohierarchical or non-hierarchical SCH.

In case that additional information is added through non-hierarchicalSCH, it is able to reconstruct the additional information by thefollowing operation.

First of all, an operation of adding additional information by atransmitting end is identically applied to the non-hierarchical SCH orother SCHs.

A receiving end is able to detect initial synchronization based onauto-correlation. And, the receiving end is able to acquire frequencysynchronization.

Subsequently, the receiving end detects a sequence index used for SCH.The receiving end performs integer-times frequency offset estimationusing the detected sequence index. The receiving end then corrects theestimated offset.

The receiving end estimates a channel using the detected sequence andthen compensates for the channel.

After completion of the channel estimation, additional information bymicro-constellation modulation is obtained.

In the fourth or fifth method of the present embodiment,micro-constellation modulation is able to use a plus phase value or aminus phase value. Namely, it is able to convert Formula 10A and Formula10B to Formula 11A and Formula 11B, respectively.

$\begin{matrix}{{P_{{bit}{(n)}} = {{\mathbb{e}}^{{- j}\frac{2\pi\; m}{X}}{p(n)}}}{{n = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{X - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 11A} \right\rbrack \\{{P_{{bit}{(k)}} = {{\mathbb{e}}^{{- j}\frac{2\pi\; m}{X}}{P(k)}}}{{k = 0},1,\ldots\mspace{14mu},{N - 1}}{{m = 0},1,\ldots\mspace{14mu},{X - 1}}} & \left\lbrack {{Formula}\mspace{14mu} 11B} \right\rbrack\end{matrix}$

And, it is able to convert Formula 10C to Formula 11C.

$\begin{matrix}{\hat{m} = {{- \frac{X}{2\pi}}\arg\left\{ {\frac{1}{N}{\sum\limits_{k = 0}^{N - 1}{{R_{eq}(k)}{P(k)}}}} \right\}}} & \left\lbrack {{Formula}\mspace{14mu} 11C} \right\rbrack\end{matrix}$

In a constellation map, a phase of each symbol (e.g., QPSK symbol, etc.)can be rotated clockwise or counterclockwise by micro-constellationmodulation.

The additional information inserting method has the followingadvantages. First of all, it is able to insert additional bitinformation without changing a previous structure. Secondly, additionalcomplexity is prevented from taking place.

The additional information added by the present method is explained asfollows.

First of all, no limitation is put on a type of the additionalinformation. And, various kinds of information for communications can beincluded. For instance, it is able to use the additional information asinformation for a length of cyclic prefix (hereinafter abbreviated CP).For instance, cyclic prefixes can be classified into short CP and longCP according to their lengths. In this case, it is able to represent atype of CP via the additional information.

And, the information may include information for an antenna mode. Inparticular, the information is able to indicate whether an antenna is asingle antenna or a multi-antenna.

Besides, various kinds of information are possible. For instance,various kinds of information such as subframe synchronizationinformation (indicating whether a first subframe of Nth radio frame or asecond subframe of Nth radio frame), BCH bandwidth (1.25 MHz or 5 MHz)and the like can be included. And, cell group ID information can beadditionally inserted.

FIG. 19 is a flowchart of a method of generating a sequence for asynchronization channel according to an embodiment of the presentinvention. FIG. 19 shows an example of P-SCH among sequences forsynchronization channels.

Referring to FIG. 19, according to the above-explained five kinds ofmethods, a sequence for a synchronization channel (e.g., P-SCH sequence,S-SCH sequence, hybrid sequence, non-hierarchical SCH sequence) isgenerated. And, additional information is then inserted in the generatedsequence (S1001). The additional information inserting step is carriedout by one of the above-explained five kinds of methods. In particular,masking for codes is used, the additional information inserting schemeusing micro-constellation modulation is used, or both of the masking andthe micro-constellation modulation are used.

The P-SCH generated by the above step is transformed into a time domainsequence by steps S1003 to S1009 corresponding to the aforesaid stepsS103 to S106 of FIG. 10 and is then transmitted to a user equipment.

A communication apparatus according to the present embodiment is able toinclude independent modules for the respective steps.

FIG. 20 is a block diagram of a transmitting apparatus according to anembodiment of the present invention.

Referring to FIG. 20, a transmitting apparatus according to anembodiment of the present invention may include a sequence generation &additional information insertion module 21 according to one of the fivekinds of methods, an FFT module 22, a DC & guard subcarrier insertingmodule 23, a PAPR scheme applying module 24 and an IFFT module 25.

And, the communication apparatus according to the present invention canbe implemented according to FIG. 21.

FIG. 21 is a block diagram of a communication apparatus for transmittingP-SCH according to the present invention.

Referring to FIG. 21, a communication apparatus for transmitting P-SCHaccording to the present invention includes a serial-to-parallelconverting unit 11, a subchannel mapping & PAPR enhancement module 12performing symbol-to-subcarrier mapping and PAPR enhancement, an IFFTmodule 13 performing IFFT, a parallel-to-serial converting module 14,and a CP inserting module 15 inserting a cyclic prefix.

An output signal by the steps S1001 to S1009 is inputted to theapparatus shown in FIG. 21 and is then transmitted to a receiving end.Yet, since the step S107 is performed by the apparatus shown in FIG. 15,if the output signal is transmitted by the apparatus shown in FIG. 21,it is able to omit the step S1007. Moreover, since an operation ofinserting the guard subcarrier in the step S1005 can be implemented by afilter (not shown in the drawing) separately provided to the apparatusshown in FIG. 21, it is able to omit the guard subcarrier insertingoperation.

Second Embodiment

First of all, a method of generating a sequence usable for asynchronization channel is explained as follows. Meanwhile, it is ableto use both of the first embodiment and the second embodiment of thepresent invention simultaneously. In particular, after a sequence isgenerated according to the second embodiment of the present invention,it is able to add additional information to the generated sequenceaccording to the first embodiment of the present invention.

A code sequence configuring a synchronization channel or a preambleincludes orthogonal or quasi-orthogonal codes having goodcharacteristics of cross-correlation. And, the preamble signal indicatesa reference signal used for such a purpose as initial synchronization,cell search, channel estimation and the like used by a communicationsystem.

For instance, in case of PI (Portable Internet, Specifications for 2.3GHz band Portable Internet Service—Physical Layer)PN codes are masked on127 kinds of sequences except a case of all zeros using 128×128Hardamard matrix and the corresponding sequences are inserted infrequency domain.

For another instance, in case of OFDM based IEEE 802.11a system, thereexists a short preamble used for AGC (automatic gain control), diversityselection, timing synchronization or coarse frequency synchronization.In the short preamble, a specific reference signal is inserted in asubcarrier corresponding to a quadruple number only (4-space interval infrequency domain). A sequence inserted with an equi-spaced interval l infrequency domain appears in time domain in a manner that a same patternis repeated l times. Such a repetitive pattern facilitates acquisitionsof timing synchronization and frequency synchronization. FIG. 22A andFIG. 22B are diagrams of frequency and time domain signals of a shortpreamble used by IEEE 802.11a, respectively. FIG. 23A and FIG. 23B arediagrams of auto-correlation characteristics of a short preamble used byIEEE 802.11a in frequency and time domains, respectively.

Preferably, there exist a number of sequences having goodcross-correlation characteristics for the discrimination of cell ormobile subscriber station (i.e., user equipment) in a mobilecommunication system. In binary Hardamard codes or polyphase CAZAC(constant amplitude zero auto-correlation) codes, a count of codesmaintaining orthogonality as orthogonal codes is limited. For instance,a count of N-length orthogonal codes, which can be converted to N×NHardamard matrix, is ‘N’, and a count of N-length orthogonal codes,which can be generated from CAZAC codes, becomes a count of naturalnumbers that are relatively prime with ‘N’ and equal to or smaller than‘N’. [David C. Chu, “Polyphase Codes with Good Periodic CorrelationProperties”, Information Theory IEEE Transaction on, vol. 18, issue 4,pp. 531-532, July, 1972]

For instance, in OFDM (orthogonal frequency division multiplexing)system, a length of one OFDM symbol normally has a length of power of 2for the fast implementations of FFT (Fast Fourier Transform) and IFFT(Inverse Fast Fourier Transform). In this case, if a sequence isgenerated using Hardamard codes, it is able to generate sequence typescorresponding to a total length. If a sequence is generated using CAZACcodes, it is able to generate sequence types corresponding to N/2. So, acount of the sequence types is limited.

FIG. 24 is a flowchart of a code sequence generating method according toone preferred embodiment of the present invention.

Referring to FIG. 24, a code sequence generating method according to onepreferred embodiment of the present invention includes a step S301 ofgenerating a unit code sequence set including a plurality of unit codesequences having a length L each by code generating algorithm accordingto a code type, a step S302 of generating a repetitive code sequence setincluding a plurality of repetitive code sequences, which have a totallength N=LN_(r), generated by repeating each of the unit code sequencesbelonging to the unit code sequence set N_(r) times, and a step S305 ofmasking each of the repetitive code sequences belonging to therepetitive code sequence set with an orthogonal code having a lengthN_(r).

The unit code sequence set generating step is the step of generating aunit code sequence set

a_(N_(seq_L) × L)having a length L of each unit code sequence and a count N_(seq) _(—)_(L) of unit code sequences. And, the unit code sequence set

a_(N_(seq_L) × L)can be represented as matrix N_(seq) _(—) _(L)×L shown in Formula 12.

$\begin{matrix}{a_{N_{{seq}\;\_\; L} \times L} = \begin{bmatrix}a_{N_{{seq}\;\_\; L} \times L}^{0} \\a_{N_{{seq}\;\_\; L} \times L}^{1} \\\vdots \\a_{N_{{seq}\;\_\; L} \times L}^{N_{{seq}\;\_\; L} - 1}\end{bmatrix}} & \left\lbrack {{Formula}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Formula 12,

a_(N_(seq_L) × L)^(k) = [a_(N_(seq_L) × L)^(k)(0)a_(N_(seq_L) × L)^(k)(1)  …  a_(N_(seq_L) × L)^(k)(L − 1)], a_(N_(seq_L) × L)^(k)is a row vector indicating a sequence of a k(=0, 1, 2, . . . , N_(seq)_(—) _(L)−1)_(th) sequence type index, and

a_(N_(seq_L) × L)^(k)(l)indicates an l(=0, 1, 2, . . . , L−1)_(th) element of a k^(th) sequence.

Two cases can be taken into consideration for a method of generating aunit code sequence set having a plurality of unit code sequences each ofwhich length is L. A first case is a method of generating a unit codesequence having a code length L by specific code generating algorithm(first scheme). A second case is a method of generating a unit codesequence having a code length L by generating a code sequence having alength L′ (L′ is a natural number greater than L.) by specific codegenerating algorithm and by eliminating (L′−L) elements from elementsconfiguring the generated sequence (second scheme). In case of CAZACcodes, it is preferable that L′ is a smallest prime number among naturalnumbers greater than L.

For the above two cases, a method of generating CAZAC code of L=256 isexplained in detail by taking an example as follows.

First of all, in the first scheme, a unit code sequence set

a_(N_(seq_L) × L)including unit code sequences of length L=256 can be generated by CAZACcode generating algorithm represented as Formula 13. [David C. Chu,“Polyphase Codes with Good Periodic Correlation Properties”, InformationTheory IEEE Transaction on, vol. 18, issue 4, pp. 531-532, July, 1972]

$\begin{matrix}{{a^{{index}{(M)}}(l)} = \left\{ \begin{matrix}{{\exp\left( {{\mathbb{i}}\frac{M\;\pi\;{l\left( {l + 1} \right)}}{L}} \right)},} & {{when}\mspace{14mu} L\mspace{14mu}{is}\mspace{14mu}{odd}} \\{{\exp\left( {{\mathbb{i}}\frac{M\;\pi\; l^{2}}{L}} \right)},} & {{when}\mspace{14mu} L\mspace{14mu}{is}\mspace{14mu}{even}}\end{matrix} \right.} & \left\lbrack {{Formula}\mspace{14mu} 13} \right\rbrack\end{matrix}$

-   -   where l=0, 1, 2, . . . , L−1

In Formula 13, M includes natural numbers relatively prime with L andindex(M)(=0, 1, 2, . . . , N_(seq) _(—) _(L)−1) indicates an index incase of aligning the M in an ascending series order. Since L=256 is aneven number, a code sequence is generated by the second expression ofFormula 13 and a code sequence count N_(seq) _(—) _(L) becomes N_(seq)_(—) _(L)=256/2=128. And, by the number of M, the code sequence count isdetermined.

In the second scheme, in order to generate a unit code sequence setincluding unit code sequences of length L=256, a unit code sequence ofL=256 is generated in a manner of generating a code sequence having alength of L′=257 by applying the CAZAC code generating algorithm likeFormula 13 to L′=257 that is a smallest prime number among naturalnumbers greater than L (substituting L′ for L in Formula 13) andeliminating an element corresponding to a 256^(th) index of thegenerated code sequence. In this case, as the unit code sequences havingthe code length of L=256 each can be generated as many as 256 (=257−1),it is able to increment the count of the unit code sequences more thanthat of the first case.

In FIG. 24, in the repetitive code sequence set generating step S303, arepetitive code sequence set

a_(N_(seq_L) × N)including repetitive code sequences of a total length N=LN_(r) isgenerated by repeating each of the unit code sequences belonging to theunit code sequence set generated by the above method N_(r) times, whichcan be represented as Formula 14.

$\begin{matrix}{{{a_{N_{seq\_ L} \times N} = \left\lbrack {a_{N_{seq\_ L} \times L}^{0},\ldots\mspace{14mu},a_{N_{seq\_ L} \times L}^{N_{r} - 1}} \right\rbrack},{where}}{a_{N_{seq\_ L} \times L}^{0} = {\ldots = {a_{N_{seq\_ L} \times L}^{N_{r} - 1}.}}}} & \left\lbrack {{Formula}\mspace{14mu} 14} \right\rbrack\end{matrix}$

If a unit code sequence having a code length of L=256 is repeatedN_(r)=4 times, a repetitive code sequence having a total code lengthN=1024 is generated. An auto-correlation characteristic of a repetitivecode sequence having a code length N is to have a peak value of N_(r)times for the length N.

In FIG. 24, the step S305 of masking the repetitive code sequence withthe orthogonal code of length N_(r) is the step of generating a finalcode sequence set

a_(N_(seq_L) ⋅ N_(seq_r) × N)by masking each repetitive code sequence belonging to a repetitive codesequence set

a_(N_(seq_L) × N)per unit a repeated unit code sequence with different type orthogonalcodes

h_(N_(seq_r) × N_(r))(e.g., Hardamard codes) having good auto-correlation characteristic anda code length of N_(r). And, the masking step can be represented asFormula 15.

$\begin{matrix}{{{a_{{N_{{seq}\;\_\; L} \cdot N_{{seq}\;\_\; r}} \times N}^{{N_{{seq}\;\_\; L} \cdot r} + k}(l)} = {{h_{N_{{seq}\;\_\; r} \times N_{r}}^{r}\left( {{floor}\left( \frac{l}{L} \right)} \right)} \cdot {a_{N_{{seq}\;\_\; L} \times N}^{k}(l)}}}\mspace{79mu}{{k = 0},1,\ldots\mspace{14mu},{{N_{{seq}\;\_\; L} - 1}\mspace{79mu}{{r = 0},1,\ldots\mspace{14mu},{N_{{seq}\;\_\; r} - 1}}\mspace{79mu}{{l = 0},1,\ldots\mspace{14mu},{N - 1}}}}} & \left\lbrack {{Formula}\mspace{14mu} 15} \right\rbrack\end{matrix}$

In Formula 15, floor(k) indicates an integer closest to a negativeinfinitive from ‘k’.

FIG. 25 is a diagram to explain a method of generating a final codesequence by masking a repetitive code sequence of a total code lengthN=1024 generated from repeating a unit code sequence of a code lengthL=256 N_(r)=4 times with 4×4 Hardamard codes.

Since the unit code sequence of N_(r)=4 is repeated in each repetitivecode sequence, if masking is carried on per unit code sequence withHardamard codes [1 1 1 1], [1 −1 1 −1], [1 1 −1 −1], and [1 −1 −1 1],four different final code sequences are generated for each repetitivecode sequence. So, assuming that a repetitive code sequence set includesN_(seq) _(—) _(L) repetitive code sequences, a finial code sequence sethas N_(seq) _(—) _(L)×4 final code sequences.

FIG. 26 and FIG. 27 show CDF (cumulative distribution function) and PDF(probability density function) of cross-correlation between a CAZAC codesequence of N=1024 generated by repeating a unit code sequence of lengthL=256 N_(r)=4 times and a final code sequence generated by making arepetitive code sequence of length N=1024 generated by repeating a unitcode sequence of length L=256 generated by the first or second schemeaccording to one preferred embodiment of the present invention N_(r)=4times with 4×4 Hardamard codes.

As can be confirmed through FIG. 26 and FIG. 27, the correlationcharacteristics of the code sequence generated by the method accordingto one preferred embodiment of the present invention are as good as orbetter than those of the code sequence according to the related art.Comparing the counts of the finally generated code sequences, the count(128) of the code sequences generated according to the present inventionis increased higher than that (first scheme-512, second scheme-1024) ofthe code sequences generated according to the related art.

FIG. 28 and FIG. 29 show CDF and PDF of cross-correlation between arepetitive code sequence of length N=1024 generated by repeating a unitcode sequence 1, 2, 4, 8 times by the first scheme according to onepreferred embodiment of the present invention and a final code sequencegenerated by masking with Hardamard codes. In this case, a count offinal code sequences that can be generated for repetition counts of allcases is 512.

FIG. 30 and FIG. 31 show CDF and PDF of cross-correlation between arepetitive code sequence of length N=1024 generated by repeating a unitcode sequence 1, 2, 4, 8 times by the second scheme according to onepreferred embodiment of the present invention and a final code sequencegenerated by masking with Hardamard codes. In this case, a count offinal code sequences that can be generated for repetition counts of allcases is 1,030 for a repetition count 1, 1,040 for a repetition count 2,1,024 for a repetition count 4, or 1,040 for a repetition count 8.

In a communication system requiring a code length N, a code sequence setof a code length N=1024 undergoes data processing into a formatrequested by the communication system and can be inserted for a use ofpreamble, pilot signal or the like. As mentioned in the foregoingdescription, in a sequence inserted with an equi-space l in frequencydomain, a same pattern appears in time domain repeatedly l times. A codesequence or code sequence set of the present invention is generated intime domain. So, if the code sequence or code sequence set of thepresent invention is used by a communication system requiring dataprocessing in time domain, the code sequence generated according to thepresent invention is used as it is. If the code sequence or codesequence set of the present invention is used by a communication systemrequiring data processing in frequency domain, the time domain codesequence generated according to the present invention can be used bybeing transformed into a frequency domain signal by DFT (DiscreteFourier Transform) or FFT (Fast Fourier Transform).

FIG. 32 and FIG. 33 are block diagrams to explain a signal transmittingmethod and a transmitting apparatus according to one preferredembodiment of the present invention, in which the technical features ofthe present invention are applied to OFDM/OFDMA/SC-FDMA based radiocommunication system. FIG. 32 is a block diagram of a transmitter andFIG. 33 is a block diagram of a receiver corresponding to thetransmitter shown in FIG. 32.

Referring to FIG. 32, traffic data and control data are inputted andthen multiplexed by a muxer 61. In this case, the traffic data isdirectly associated with a service provided by a transmitting side to areceiving side and the control data indicates data inserted to controlthe transmitting and receiving sides to perform communications with eachother smoothly. A code sequence generated by the above technicalfeatures of the present invention is a sort of control data and can beinserted for the use of initial synchronization acquisition, cell searchor channel estimation by the receiving side. A position in which thecode sequence is inserted may vary according to a communication system.For instance, in IEEE 802.16 broadband wireless access system, the codesequence can be inserted in a form of preamble or pilot signal. In casethat a multi-antenna (MIMO) system is applied, it is able to insert thecode sequence in a form of midamble.

Input data including the traffic data and the control data undergoeschannel coding by a channel coding module 62. Channel coding is aprocess for adding parity bits to enable the receiving side to correctan error occurring in the course of transmission of a signal transmittedby the transmitting side. And, convolution coding, turbo coding, LDPC(low density parity check) coding or the like can be used for thechannel coding.

The data channel-coded by the channel coding module 62 undergoes digitalmodulation through symbol mapping according to algorithm such as QPSK,16QAM and the like by a digital modulating module 63.

Data symbols through the symbol mapping undergo subchannel modulation bya subchannel modulating module 74, are mapped to each subcarrier of anOFDM or OFDMA system, and are then transformed into time domain signalsaccording to IFFT conducted by an IFFT module 65.

The IFFT-transformed data symbol undergoes a filtering process by afilter 66, is converted to an analog signal by a DAC module 67 m isconverted to an RF signal by an RF module 68, and is then transmitted tothe receiving side through an antenna 69.

Alternatively, according to a type of a generated code (e.g., CAZACcode), channel coding or symbol mapping of a specific code sequence isomitted. And, the specific code sequence is mapped to a subchannel bythe subchannel modulating module 64 and then transmitted through thesubsequent data processing steps.

Referring to FIG. 33, a receiver reconstructs the received data througha process reverse to the data processing of the transmitter and thenfinally obtains the traffic data and the control data.

The configurations of the transmitter and receiver shown in FIG. 32 andFIG. 33 are just exemplary to help the understanding of the technicalfeatures of the present invention. And, it is apparent to those skilledin the art that the data processing method for the receiving side totransmit the code sequence for the use of initial synchronizationacquisition, cell search or channel estimation can be achieved invarious ways known to public.

A code sequence or code sequence set according to the present inventionis applicable to a CDMA based wireless mobile communication system bythe mobile communication standardization organization such as 3GPP,3GPP2 and the like or a wireless internet system by Wibro or Wimax in amanner of being transmitted to a receiving side after having beendata-processed by a transmitting side according to a system requested bythe corresponding system.

INDUSTRIAL APPLICABILITY

Accordingly, the present invention provides the following effects.

First of all, the present invention proposes a method of generating asynchronization channel carrying additional information.

Secondly, information can be provided to a user equipment via thesynchronization channel without increasing complexity.

Thirdly, the present invention is able to use the related artsynchronization estimating method.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting a signal in a wirelesscommunication system, the method comprising: transmitting a referencesignal sequence to a receiving end, wherein: the reference signalsequence is given by repeating a base sequence at least twice andmasking the repeated base sequence with an orthogonal code, the basesequence is CAZAC (constant amplitude zero auto-correlation) code, andthe masking the repeated base sequence with the orthogonal codecomprises multiplying each base sequence of the repeated base sequencewith a corresponding value of the orthogonal code.
 2. The method ofclaim 1, wherein the orthogonal code is Hadamard code.
 3. The method ofclaim 1, wherein the base sequence having a code length of L isgenerated by eliminating elements of a specific code sequence having acode length of M, the specific code sequence being generated by a codegenerating algorithm, and wherein M is a smallest prime number greaterthan L, and L and M are natural numbers.
 4. The method of claim 3,wherein the code generating algorithm is represented${a^{{index}{(A)}}(n)} = \left\{ \begin{matrix}{{\exp\left( {{\mathbb{i}}\frac{A\;\pi\;{n\left( {n + 1} \right)}}{M}} \right)},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{odd}} \\{{\exp\left( {{\mathbb{i}}\frac{A\;\pi\; n^{2}}{M}} \right)},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{even}}\end{matrix} \right.$ as where n=0, 1, 2, . . . , M−1 wherein A and Mare natural numbers relatively prime, and wherein index(A)(=0, 1, 2, . .. , N_(seq M)−1) indicates an index in case of aligning A in anascending series order.
 5. The method of claim 1, wherein the orthogonalcode has a length equal to the number of repeating the base sequence. 6.An apparatus for transmitting a signal in a wireless communicationsystem, the apparatus comprising: a radio frequency (RF) moduleconfigured to transmit a reference signal sequence to a receiving end inthe wireless communication system, wherein: the reference signalsequence is given by repeating a base sequence at least twice andmasking the repeated base sequence with an orthogonal code, the basesequence is CAZAC (constant amplitude zero auto-correlation) code, andthe masking the repeated base sequence with the orthogonal codecomprises multiplying each base sequence of the repeated base sequencewith a corresponding value of the orthogonal code.
 7. The apparatus ofclaim 6, wherein the orthogonal code is Hadamard code.
 8. The apparatusof claim 6, wherein the base sequence having a code length of L isgenerated by eliminating elements of a specific code sequence having acode length of M, the specific code sequence being generated by a codegenerating algorithm, and wherein M is a smallest prime number greaterthan L, and L and M are natural numbers.
 9. The apparatus of claim 8,wherein the code generating algorithm is${a^{{index}{(A)}}(n)} = \left\{ \begin{matrix}{{\exp\left( {{\mathbb{i}}\frac{A\;\pi\;{n\left( {n + 1} \right)}}{M}} \right)},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{odd}} \\{{\exp\left( {{\mathbb{i}}\frac{A\;\pi\; n^{2}}{M}} \right)},} & {{when}\mspace{14mu} M\mspace{14mu}{is}\mspace{14mu}{even}}\end{matrix} \right.$ represented as where n=0, 1, 2, . . . , M−1wherein A and M are natural numbers relatively prime, and whereinindex(A)(=0, 1, 2, . . . , N_(seq M)−1) indicates an index in case ofaligning A in an ascending series order.
 10. The apparatus of claim 6,wherein the orthogonal code has a length equal to the number ofrepeating the base sequence.